Observation Of Temperature In Reservoirs And Simulation Of Temperature Recovering In The Downstream Of A Dam

The reservoir is an artificial lake or pond created by dams in the river,which can store or lock a large amount of water in upstream areas.It has a range of functions like controlling flood,generating power and so on.In reservoirs with large capacity and strong adjusting function,there may exist regular temperature stratification along the vertical direction due to the water storing.On the one hand,this stratification can lead to a stratification of local aquatic organisms’ distribution.On the other hand,the abnormally cold water discharged from the reservoir can have negative effect on downstream fishes’ reproduction and crops’ growth.In order to govern the environmental problem caused by the temperature stratification in reservoirs,it’s necessary to study the phenomenon and to understand the mechanisms.In order to control the ecological problems caused by reservoir construction and operation,it is necessary to understand the water temperature stratification phenomenon in the reservoir and the post-dam temperature recovery.However,due to the complexity of water temperature exchange problems,the critical conditions of water stratification still need to be further clarified.In this thesis,the temperature stratification in large reservoirs was studied by experimental tests as well as numerical simulations.First,the author designed and constructed an experimental device in which the temperature distribution of the water was measured with respect to time.Meanwhile,a numerical model to simulate the temperature stratification in reservoirs was established using Telemac-3D software.The numerical model was modified and validated by the collected experimental data.With the model,a series cases with different inflow conditions were simulated to survey the development of temperature stratification in reservoirs.In this thesis,the development of temperature stratification in reservoirs was observed and measured during the experiments.When stable stratification occurred,the water can be divided into thermostat layer,thermocline and isothermal layer from the bottom to the top.The simulated results were consistent with the experimental results,indicating that the established numerical model was reliable to study the temperature stratification problems.According to the modelling results of water temperature stratification under different inflow conditions,the value of Richardson number was a key parameter to justify whether the temperature field was well-mixed or stratified.In this study,the critical Richardson number is 0.25.Finally,an engineering case was modelled with Telemac-3D software,where temperature recovering of the cold water discharged from the Baise Dam on May was simulated along the downstream river.The simulating results of the engineering case shows that the temperature rising rate was very low in the whole domain except the confluence of Chengbi River,where the water temperature is a bit high.Compared with in the upstream reach,the rising rate of water temperature was even lower in the downstream reach near Baise.